MIL-DTL-55535A
4.8.2 Impedance. The impedance of the earphone shall be measured with 0.122 volt at 1,000 Hz
applied to the earphone terminals. The impedance shall be determined either by measuring the voltage
across and the current through the earphone or with an impedance bridge. The impedance of the
earphone, when mounted on the coupler, shall meet the requirements of 3.7.5.
4.8.3 Distortion test. The earphone shall be mounted on the 6 cc coupler, and shall be connected to
the test circuit specified in 4.8.1.1. The output of the oscillator shall be adjusted to 2.12 volts rms at 300
Hz across the series combination of the 15 ohm resistor and the earphone. The rms harmonic distortion
shall be measured with a Hewlett-Packard Model 330-C Total Noise Distortion Meter, or equal, connected
across the output of the microphone referenced in 4.8.1. The distortion measurement shall be repeated
at 400 Hz and at sufficient points between 400 and 3,500 Hz to determine the frequency where maximum
distortion exists. Total harmonic distortion shall meet the maximum requirements of 3.7.2.
4.8.4 Overload. After operation of the earphone for 8 hours with 500 milliwatts input power (2.74 volts)
at 1,000 Hz, the response shall be tested as specified in 4.8.1, to establish compliance with the
requirements of 3.7.3.
4.8.5 Dielectric strength and insulation resistance test. The earphone shall be subjected to a voltage
of 100 volts dc for 10 seconds applied between the terminals of the earphone and the insulated outer
metal parts of the earphone. The earphone shall be tested for compliance with 3.7.4.
4.9 Operational test (see 3.11). Prior to packaging, completely assembled units shall be tested by a
talk test to insure correct wiring and satisfactory operation.
4.10 Visual and mechanical inspection. The equipment shall be examined for the defects specified in
MIL-STD-252.
4.11 Inspection for dimensional interchangeability (see 3.12). Each replaceable part listed below in the
selected Transducer Equipments shall be interchanged with the corresponding part in the approved first
article sample in sequential order. At the completion of this inspection, the interchanged parts shall be
reassembled in their original transducer equipments.
a. Switch housing.
b. Microphone boom.
c. Earphone elements.
4.12 Switch life. A series circuit shall be set up including a 24 volt dc supply, a resistive load, and the
switch. During the test, one-half ampere shall flow in the control circuit, and 60 milliamperes shall flow in
the microphone circuit of the switch. The switch shall be tested to determine compliance with 3.9,
following 100,000 complete cycles. One cycle of switch operation test shall consist of the following, in
sequence:
a.
Switch in mid-position.
b.
Switch in forward position.
c.
Switch in mid-position.
d.
Switch in back position.
e.
Switch in mid-position.
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